From a Buddhist perspective it doesn't make much sense to talk about mental illness. Mental illnesses are narrow intellectual concepts that create a sense of identity and Buddhism is about not attaching yourself to labels. The Buddhist ideal is simply to show compassion to everyone.

At the same time a concept like depression can have some use. Depression is more than just being unhappy. If you use it to simply mean the opposite of happy you devoid it from meaning. It's a cluster of symptoms. Having the concept allows us to research that cluster and come up with things that aren't obvious.

So what is the truly proper attitude? Give up all kinds of censure and criticism?

Give criticism based on the utility of the effect of giving criticism. If you give someone constructive feedback that allows him to improve, that criticism is good. Censure is similar. If someone violates social norms punishing him was disapproval is useful to enforce those social norms.